The term "standard resistance" or "standard running resistance" is herein used to mean any force which opposes the motion of an automotive vehicle which is driven to keep rolling over the surface of a flat road having 0% gradient at a constant vehicle speed. The term "running resistance" is herein used to mean any force which opposes the motion of an automotive vehicle which is driven to keep rolling over the surface of a road at a constant vehicle speed. Running resistance is equal to standard resistance if an automotive vehicle is driven to keep rolling over the surface of a flat road having 0% gradient at a constant vehicle speed. Running resistance increases and becomes greater than standard resistance if the automotive vehicle is accelerated to increase speed from the constant vehicle speed. The term "acceleration resistance" is herein used to mean this increment or difference in running resistance that has occurred due to acceleration. Running resistance is greater when the automotive vehicle is driven to keep rolling over the surface of a flat road having gradient greater than 0% at a constant vehicle speed than standard resistance for the same vehicle speed. The term "gradient resistance" is used to mean this increment or difference in running resistance.
JP-A 9-242862 discloses a vehicle control system in which a speed ratio between an input shaft and an output shaft of an automatic transmission is controlled in response to road gradient, throttle opening degree, and vehicle speed. In order to estimate road gradient of a road, over which the vehicle is rolling, a road gradient torque (T.alpha.) is determined by subtracting from a driving torque (To) a sum of a flat road running resistance torque (Tr) and an acceleration resistance torque (T.alpha.). A characteristic of variation of flat road running resistance torque (Tr) against variation of vehicle speed is mapped. This mapped data are retrieved using a current reading point of vehicle speed to give a value of flat road running resistance torque (Tr).
An assignee to which the present invention is to be assigned filed as an applicant Japanese Patent Application No. 10-199894 in Japan on Jul. 15, 1998. This Japanese Patent Application does not form prior art under 35 U.S.C. 102 and 35 U.S.C. 103, and it does not form the state of the art under Article 54(2) EPC.
Japanese Patent Application No. 10-199894 discloses a vehicle control system for an automotive vehicle including an internal combustion engine and a continuously variable transmission (CVT). The control system determines an ordinary input shaft speed against operator manipulation of an accelerator pedal and vehicle speed. The ordinary input shaft speed is an input shaft speed of the CVT against the current operator manipulation of accelerator and vehicle speed for supporting the motion of the automotive vehicle, which is rolling over a flat road having 0% gradient at the current vehicle speed. The control system determines a gradient resistance (force) and sets a portion, less than 100%, of the determined gradient resistance force as a driving force correction. The control system corrects the determined ordinary input shaft speed by an amount corresponding to the driving force correction.
The vehicle control systems mentioned above are satisfactory to some extent. Need remains to further develop the vehicle control systems by enhancing accuracy with which standard resistance (a flat road resistance torque, for example) is approximated.
Standard resistance may be approximated using the magnitude of deceleration during the inertia motion of an automotive vehicle that is rolling over a flat road having 0% gradient. This approximation technique is known as "coast down technique." Alternatively, the standard resistance may be determined as a quadratic function of vehicle speed during the inertia motion of an automotive vehicle that is rolling over a flat road.
Driving an automotive vehicle to keep rolling over a flat road having 0% gradient, there occurs resistance due to frictional loss in power train and in accessory drive. If values of standard resistance approximated using the coast down technique have been stored, a microcomputer-based controller may attribute the above-mentioned resistance due to the frictional loss to road gradient irrespective of the fact that the automotive vehicle is rolling over a flat road. This might cause the controller to increase driving force irrespective of the fact there is no road gradient, degrading a drive feel during driving an automotive vehicle over a flat road.
FIG. 11 is a schematic view of a conventional CVT of the V-belt type. The CVT comprises a primary pulley 30, a secondary pulley 36, and a V-belt 35 interconnecting the pulleys 30 and 36, Each of the pulleys 30 and 36 grips the V-belt 35 for transmission of power. The pulleys 30 and 36 have displaceable pulley halves 31 and 37 and servo chambers 34 and 39, respectively. The pulley haves 31 and 37 are forced into frictional engagement with the V-belt 35 in response to levels of hydraulic pressure PR and PL fed to the servo chambers 34 and 39. The levels of hydraulic pressure PR and PL are determined by operating conditions, which are defined by a shift range position, operator manipulation of accelerator pedal, and vehicle speed.
According to the coast down technique, a neutral (N) range is selected to accomplish the inertia motion of an automotive vehicle that is rolling over a flat road having 0% gradient. In the N range, the levels of hydraulic pressure PR and PL within the servo chambers 34 and 39 drop to the lowest.
The vehicle operator depresses the accelerator pedal to drive the automotive vehicle to keep rolling over the flat road at a constant vehicle speed. Under this condition, the levels of hydraulic pressure PR and PL within the servo chambers 34 and 39 are always greater than the lowest level.
The displaceable pulley halves and stationary pulley halves, which are biased into frictional engagement the V-belt 35, are slightly deformed due to increased friction force and hydraulic pressure PR and PL so that the centerline of the V-belt 35 deviates by .DELTA..theta.. This deviation .DELTA..theta. causes an increase in friction.
Friction force caused by engagement of the pulleys with the V-belt and friction due to the deviation .DELTA..theta. may cause a microcomputer-based controller to attribute this friction to road gradient if standard resistance determined by coast down technique is used. The controller may increase driving force in response to the increased friction than expected by the vehicle operator,
In an automatic transmission of the gearing type, levels of hydraulic pressure developed within each of torque transmitting friction units for drive (D) range are higher than those for neutral (N) range. Thus, there is an increase in running resistance during driving with D range over the surface of a flat road. This increase in running resistance is caused by a pumping loss to accomplish an increase in hydraulic pressure from the level for the N range to the level for the D range and by friction of rotary elements that are engaged.
An object of the present invention is to provide a process of forming, with good accuracy, a characteristic on which a value of standard resistance of an automotive vehicle lies.
Another object of the present invention to provide a vehicle control system for an automotive vehicle, which is free from any variation in driving force unexpected by an operator.